The present invention relates to an internal combustion engine, and more specifically to a diagnostic system or method for a feedback fuel pressure control system for an engine, such as a direct injection type engine or a lean burn engine.
Recently, the technique of in-cylinder direct fuel injection in a spark ignition engine such as a gasoline engine is under development to improve the fuel efficiency by selectively using stratified charge combustion in a partial load region. In a conventional engine of a type injecting gasoline into the intake port, the air fuel mixture is transported to the combustion chamber. By contrast, a direct injection type engine can avoid adverse influence of transportation (distance/velocity) lag of fuel, on transient driving performance, and emission performance.
A direct injection engine of one conventional example is equipped with a high pressure fuel pump for increasing the fuel pressure for efficient fuel atomization, and a fuel pressure sensor used for feedback-controlling the fuel pressure to a desired fuel pressure determined in accordance with engine operating conditions. (as disclosed in Japanese Utility Model Provisional (Kokai) Publication No. 5(1993)-69374; "TOYOTA CORONA PREMIO", New Model Manual, September 1996, pages 1.about.59; or Japanese Patent Provisional (Kokai) Publication No. 5(1993)-321783).